Abiotic and Biotic Correlates of Hooded Merganser and Wood Duck Nest Box Usage
by:
Megan Carroll
A senior thesis submitted in partial fulfillment of the requirements for the degree of
Bachelor of Science
Wildlife and Fisheries Management
At
Unity College
Fall, 2017
i
Abiotic and Biotic Correlates of Hooded Merganser and Wood Duck Nest Box Usage
by:
Megan Carroll
A senior thesis submitted in partial fulfillment of the requirements for the degree of
Bachelor of Science
Wildlife and Fisheries Management
At
Unity College
Fall, 2017
ii
Abstract
Wildlife managers use a variety of management practices to properly sustain harvested
wildlife species in the face of a constantly changing environment. Wood Duck and Hooded
Merganser nest box usage in Connecticut has varied throughout the years 2005–2016. The
overall objectives of this study were to examine potential relationships between weather
variables and species nest box usage in Connecticut and to determine if environmental factors
could predict species usage in the future. Data supplied by the Connecticut Department of
Environmental and Energy Protection and collected from Weather Underground (2017) and
Google Earth Pro (2017) were analyzed using least squares regression and correlation models.
Weather information (winter, spring, 6-month precipitation and temperature), elevation, distance
to coast, and competition usage were compared. Hooded Merganser nest box usage gradually
increased while Wood Duck usage showed a slight decrease. Distance from the coast was
significant for Wood Duck usage. Hooded Merganser nest box usage was found to be inversely
related to winter precipitation. Nest box usage for both species decreased when competition from
mammals and other birds was added. A slight influence of weather variables on nest box usage
was noted, but it cannot be concluded that weather is a good predictor. Nest box placement and
dump nesting possibly contribute to the strong negative relationship amongst competitively
nesting species. To combat this, managers need to ensure nest boxes are properly hidden along
water bodies with sufficient cover to reduce parasitic nesting.
iii
Acknowledgements
I want to thank my advisors, Kevin Spigel and Matthew Chatfield, for taking time out
their schedules to meet weekly and work through every problem I encountered from the
beginning. Their encouragement, humor, understanding, and knowledge helped me through this
past year develop a working thesis. Second, Aimee Phillippi for reviewing every single one of
my drafts and being flexible throughout the process as my professor as well. Third, Brent Bibles
for constant encouragement as well as answering every question, even though it was not
required. Fourth, Connecticut State Biologist Kelly Kubik for originally sparking my interest in
the topic studied, expressing interest, and supplying the waterfowl data. Fifth, my roommates,
Amanda Griswold and Cassidy Marshall for assisting in the early stages of data organization and
GIS assistance. Lastly, Cole Arsenault, Greg LcClair, Marlea Naples, Wesley Franco, and family
for providing moral support through the past year.
iv
Table of Contents
LIST OF TABLES ............................................................................................................................. V
LIST OF FIGURES .......................................................................................................................... VI
INTRODUCTION ............................................................................................................................... 1
METHODS ........................................................................................................................................ 7
DATA COLLECTION ................................................................................................................................... 7
DATA ANALYSIS ......................................................................................................................................... 9
RESULTS ........................................................................................................................................ 10
DISCUSSION ................................................................................................................................... 16
LIMITATIONS TO STUDY ............................................................................................................................ 20
FUTURE STUDIES ................................................................................................................................... 21
CONCLUSION AND MANAGEMENT IMPLICATIONS .............................................................. 22
REFERENCES ................................................................................................................................ 23
v
List of Tables
Table 1. Correlation Coefficients for Weather Variables and Nest Box Usage ………………15
vi
List of Figures
Figure 1. Wood Duck and Hooded Merganser Distribution in North America ……………...….2
Figure 2. ArcGIS Map of Sites and Weather Stations …………………………..……………….3
Figure 3. USDA Connecticut Plant Hardiness Zones …………………………………………....4
Figure 4. Wood Duck and Hooded Merganser Usage Over Time ……………………………...10
Figure 5. Wood Duck Correlation Graphs ………………………………………….…………..11
Figure 6. Hooded Merganser Correlation Graphs ………………………………………………12
Figure 7. Wood Duck Line Graphs ……………………………………………………………..14
Figure 8. Hooded Merganser Line Graphs ……………………………………………………...1
1
Introduction
Wildlife managers rely on a variety of management practices in order to properly sustain
harvested wildlife species in the face of a constantly changing environment. Hunting is a
widespread management tactic utilized to maintain a healthy population because it is cheap,
effective, and involves the general public. It is crucial for wildlife biologists to avoid high
harvest quotas that could result in additive mortality since an overharvested population will not
be able to sustain itself over time (Sandercock et al. 2011). Large population sizes and numerous
stakeholders in North America result in waterfowl being extensively studied (Batt et al. 1992).
Lengthy regulatory processes require data collection on population sizes, harvest levels,
production, and migration in order to pass new regulations (Johnson and Williams, 1995).
Despite the large investment in studying these biotic factors influencing population sizes, abiotic
factors, such as weather, historically have been overlooked in population assessment practices
(Heusamnn, 1984). More recently, adaptive waterfowl harvest management techniques have
been introduced which are based on well-defined objectives that account for uncertainty like
uncontrolled environmental factors, such as storms or other weather events (Johnson and
Williams, 1995).
Waterfowl are organized into two functional groups. Dabbling ducks, like Wood Ducks
(Aix sponsa), Blue-Winged Teal (Anas discors) and Mallards (Anas platryhynchos), feed off the
water’s surface. Diving ducks, like Hooded Mergansers (Lophodytes cucullatus), Buffleheads
(Bucephala albeola), and Ring-Necked Ducks (Aythya collaris), swim underwater to find food.
Wood Duck populations are found in eastern and western ranges, divided by the Great Plains and
multiple deserts (Fielder, 2000). Their breeding ranges are found in more northern areas, some of
which overlap with their year-round habitat, but can also be found breeding in southern regions
2
(Figure 1). Naturally occurring breeding habitat is found throughout southern parts of Canada
and extends south to Florida on the east coast, and along the shoreline of California on the west
coast. Although arrival times may vary between states, Wood Ducks are present in Connecticut
from March to November. The breeding season can begin in early March, but generally will not
start until April (Fielder, 2000; DEEP, 2012). Wood Ducks are well distributed throughout North
America while Hooded Mergansers are less commonly found (Heusmann et al. 2000). With
breeding and wintering distributions similar to those of Wood Ducks, Hooded Mergansers are
found in the same habitats, but generally in lower densities (Morse et al. 1969; Heusmann et al.
2000). Hooded Merganser breeding ranges extend throughout the east and the Pacific Northwest
but can be found regularly in the Great Lakes region (Figure 1). In Connecticut, Hooded
Mergansers begin nesting in late February to April (Morse et al. 1969).
Figure 1. Wood Duck and Hooded Merganser distribution and migratory patterns throughout North America.
Noting the similar coverage year-round (purple) along the East Coast. Maps modified from Cornell Lab of
Ornithology; data courtesy of NatureServe.
3
Wood Ducks and Hooded Mergansers are both cavity nesting species and require wooded
nesting sites close to water, with trees .3048-.6096 meters in diameter with pre-formed cavities
(Cornell University, 2015). Appropriate breeding sites consist of forested wetlands with trees
that provide cavities necessary for nesting and offer the birds with adequate cover (e.g., fallen
trees, shrubs, herbaceous plants). Areas with 50-75% cover are preferred to allow adequate
forage but also avoidance from predation (Cornell University, 2015). Both species nest near
bodies of water due to diets compromised heavily on aquatic plants and invertebrates (Fielder,
2000; Heusmann et al. 2000). Wood Duck diet varies seasonally, but includes acorns, panic grass
(Panisum), pondweed (Potamogeton), duckweed (Lemnoideae), and white waterlily (Nymphaea
alba) year-round (Drobney, 1980). Before egg-laying, females feed on invertebrates in major
taxonomic groups, such as Odonata, Diptera, Lepidoptera, Hemiptera, and Isopoda because they
are rich in calcium and protein (Drobney, 1980). Because of their feeding behavior, the Hooded
Merganser’s diet primarily consists of fish, crayfish, aquatic insects, amphibians, and some
vegetation (Dugger et al. 1994).
Both species pair with their mates before reaching the desired nesting site. Females make
the final nest selection primarily based on proximity to water (Morse et al. 1969). Male Wood
Ducks accompany their mates when searching for a cavity, but wait nearby while females
investigate each hole (Manlove and Hepp, 2000; Fielder, 2000); male Hooded Mergansers are
not known to play a role in nest selection (Dugger et al. 1994).
Due to extended hunting seasons, market shooting, and habitat loss in the early 1900s,
Wood Ducks were close to extinction in North America (DEEP, 2012). Hooded Mergansers also
suffered a decrease in population size around the same time as a result of logging, which reduces
nesting cavities (Dugger et al. 1994). With the aid of the Migratory Bird Treaty Act in 1918,
4
commercial hunting was banned, hunting seasons were not to exceed 3.5 months, and bag limits
were adjusted (Johnson and Williams, 1999). Management efforts, including the installation of
nest boxes and restoration of habitat, have boosted both species’ populations (DEEP, 2012) and
allowed for expansion throughout their historic ranges (Dugger et al. 1994).
Natural cavities are formed by woodpeckers and natural decay in large deciduous trees
found in old growth woodlots (Fielder, 2000). In most cases, these cavities are short-lived
because host trees are often blown down by strong winds or are taken by other species, leaving
cavity-nesting ducks with minimal nesting sites. To combat this issue, nest boxes are used as an
inexpensive substitution to support waterfowl populations such as Hooded Mergansers, common
mergansers, Wood Ducks, common golden eyes, barrow’s golden eyes, and buffleheads (Porter
et al. 2008). Nest boxes substitute for natural cavities and expand breeding sites, resulting in
increased Wood Duck and Hooded Merganser populations (Bellrose et al. 1964; DEEP, 2012).
Nest box installation is not limited to state agencies and biologists; many private property
owners, the majority of stakeholders, have participated in the conservation practice. The extra
nesting sites have created natural competition by other cavity nesting species posing an issue for
target species management. For example, in Arrowwood National Wildlife Refuge in North
Dakota, nest boxes were erected in 1968 to support a newly added population of hand-reared
Wood Ducks into the area (Doty et al. 1984). The birds became an established breeding
population and prominent on the refuge by 1969. The Wood Duck population continued to rise
until 1975 when it began to decline. Hooded Mergansers were first recorded using the nest boxes
in 1973 and by 1982 their nesting attempts surpassed the Wood Duck. Dual nesting, separate
individuals laying eggs in the same nest, began in 1977 and rapidly increased. Hooded
Mergansers are known to lay eggs in nests that belong to both other mergansers and Wood
5
Ducks. Data suggest mergansers became the dominant species in the refuge following the
addition of next boxes (Doty et al. 1984).
Nest boxes are only one habitat related factor that can impact waterfowl population
numbers. For example, the Massachusetts Division for Fisheries and Wildlife analyzed data
covering years 1979 to 1998 and found a 289% increase in hatching success and a 225% increase
in population size. The agency attributed this growth to changes in hunting regulations, improved
habitat, and a rise in beaver populations which resulted in more, small wooded ponds that extend
ideal foraging habitat (Heusmann et al. 2000). Biotic factors such as these are commonly a part
of by management practices in order to alter a targeted species population. In some cases,
controlling biotic factors may have no overall effect.
Unusual weather conditions may also impact duck populations and, as a result, influence
management plans. For example, the effects of abnormal weather on Wood Duck production
during 1982 in Massachusetts led to a decline in reproductive success. Abnormal weather events
in this study were defined as late snowstorms, heavy rainfall, and prevailing cold temperatures.
The decline in reproductive success was evident through smaller broods, which were caused by
reduced nest success and fewer eggs hatching in successful nests (Heusmann, 1984).
While several small storms can have a negative impact on the nest success of local
waterfowl, weather events covering a larger area will impact multiple waterfowl species’
breeding populations. For example, Mallory et al. (2003) evaluated trends in population size and
reproductive success of waterfowl species in northwest Ontario, Canada. The team used existing
waterfowl and weather data to determine if annual or regional weather conditions can cause
variation in annual estimates of waterfowl breeding populations. Weather variables explained 9–
17% of variation in abundance of dabbling ducks with higher duck abundance in years with
6
cooler February and April temperatures and higher April precipitation. For diving ducks, weather
variables explained 12–36% of variation in abundance with higher populations in years when
April was cool and February was relatively dry. Overall, weather conditions in the winter and
early spring explain some variation in annual estimates of breeding waterfowl. This study shows
that the incorporation of regional weather data into population models may provide correction
factors for waterfowl estimates and, in turn, allow managers to have a better understanding of
population trends.
Wood Duck and Hooded Merganser nest box usage in Connecticut varied throughout the
years 2005–2016, specifically with an observed increase in the Hooded Merganser population.
This increase can also be observed in Maine, New York, New Hampshire, and Vermont
(Heusmann et al. 2000). There has been no recent research suggesting why this fluctuation has
occurred or what could be the driving factors. Variation in temperature and precipitation in
months preceding nesting season has negatively influenced the abundance of waterfowl as seen
in multiple studies causing these variables to be a concern for future management purposes
(Mallory et al. 2003; Heusmann, 1984; Schummer et al. 2010). The overall objectives of this
study were to examine potential relationships between weather variables and species nest box
usage in Connecticut and to determine if environmental factors could predict species usage in the
future.
7
Methods
Data collection
The nest box data used for this study were collected by biologists and volunteers from
2005–2016 during winter months and provided by the Connecticut Department of Environmental
and Energy Protection (DEEP). Monthly temperature averages and monthly sum of precipitation
for the years 2005–2016 were collected from Weather Underground (2017) from 14 weather
stations in Connecticut, Rhode Island, Massachusetts, and New York (Figure 2). Precipitation
data were recorded from rainfall and rainfall equivalent in snow since there was no specified
form listed. Distance to the coast and elevation data were recorded for each site using Google
Earth Pro (2017).
Data consisted of the following information for each nest box: town, site, district, box
number, years checked, and years used. There were 163 sites located throughout the state of
Connecticut that were analyzed. Boxes were considered used if any sign of life was noted
Figure 2. ArcGIS map of FAA weather stations (X) and nest box sites (dots) located across the state
of Connecticut.
Atlantic Ocean
NY
MA
RI
8
including broken or whole eggs, down, membranes, and/or dead chicks. Due to inconsistent data
collection records, data were standardized by combining all nest boxes within a site. To maintain
the integrity of the original data set, majority use of a given species (51%) was used as an
organization technique. By condensing the boxes at each site and classifying each year by a
given species use, a more complete record was developed. Weather data were condensed into
two seasons: winter (December, January, February) and spring (March, April, May).
Temperatures were averaged within each season and the sum of precipitation was found.
Coordinates for each site and weather station were entered into ArcGIS and analyzed. Using
Thiessen polygons were created to assign each site to the closest weather station. A map created
by the United States Department of Agriculture (USDA) indicating plant hardiness zones in
Connecticut naturally divides the state by average annual extreme minimum temperatures
(Figure 3). These zones allowed the comparison of trends in the data to weather patterns.
Figure 3. Plant hardiness zones of Connecticut and Rhode Island as described by the average annual extreme
minimum temperatures between years 1976 to 2005 (USDA, 2012).
9
Data analysis
Least squares regression was used to calculate possible climate predictors for Wood
Ducks and Hooded Mergansers. This test was chosen to help determine changes in nest box use
by the remaining abiotic and biotic variables because of its ability to predict future values for one
variable when another’s value is unknown. By condensing the use (Wood Duck, Hooded
Merganser, other bird, mammal, no use) for each site into a proportion, years where data was not
collected were removed. Weather information (winter, spring, 6-month precipitation and
temperature) were treated as independent variables along with elevation, distance to coast, and
competition usage. The resulting p-values from this test were assessed at an alpha-level of .05.
Seasonal weather variables and waterfowl nest box usage were compared to evaluate any
possible correlations over time. Although a small dataset of only twelve records was used, the
resulting graphs gave a visual of any trend through the years. First Hooded Merganser and Wood
Duck usage were compared to understand how the two species have interacted throughout the
years. Next, graphs were created for both to show individual relationships between usage and
each weather variable. A correlation analysis verified any possible relationship. The data was
graphed and analyzed on excel, using the function “correl” to determine the correlation
coefficients. Each correlation coefficient was compared to the Pearson correlation coefficient of
.576 found based on 12 ordered pairs.
10
Results
Hooded Merganser and Wood Duck nest box usage did not show a significant correlation
between 2005–2016 (Figure 4). Wood Duck usage was consistently higher than Hooded
Merganser, but Hooded Merganser usage seemed to be increasing. Wood Duck usage remains
stable after 2008 while Hooded Merganser usage experiences more variability. The two greatest
annual increases in usage by mergansers are accompanied by large decreases in Wood Duck
usage as seen in years 2008 and 2014.
The results from the least squares regression model from Wood Duck nest usage with
weather, environmental, and competition factors, showed Hooded Merganser (t = -3.63; p =
0.0004), mammal (t = -5.68; p = <0.0001), other bird (t = -5.43; p = <0.0001), and distance to
coast (t = -2.52; p = 0.0128) were significant. Spring precipitation was not considered significant
with a p-value of 0.1889 but exhibited a weak negative trend (Figure 5). All significant variables
found in this test have a strong inverse relationship with Wood Duck nest box usage. As
competition usage and miles from coast increase, Wood Duck usage decreases (Figure 5). This
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Nest Box Usage
Figure 4. Wood Duck (dashed) and Hooded Merganser (solid) usage over
11
model resulted in a final equation where Wood Duck usage (w) can be predicted by Hooded
Merganser usage (h), mammal usage (m), other birds’ usage (b), and distance to coast (d).
Equation 1. w= -(0.347) h + -(0.798) m + -(0.556) b + -(.008) d + 1.894
The report for Hooded Merganser usage consisting of weather, environmental, and
competition factors resulted with Wood Duck (t = -3.63; p = 0.0004), mammal (t = -2.61; p =
0.0100), other bird (t = -3.19; p = 0.0017), and winter precipitation (t = -2.50; p = 0.0136) as
significant at the alpha-level of 0.05. All variables associated with Hooded Merganser usage
R² : 0.139*
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 20 40 60 80
Wood Duck Usage
Distance to Coast (mi)
R² : 0.007
0.0
0.2
0.4
0.6
0.8
1.0
1.2
75 95 115 135 155
Wood Duck Usage
Winter Precipitation (in)
R² : 0.099
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 500 1000 1500 2000
Wood Duck Usage
Elevation (ft)
R² : 0.022
0.0
0.2
0.4
0.6
0.8
1.0
1.2
95 105 115 125 135 145
Wood Duck Usage
Spring Precipitation (in)
R² : 0.072
0.0
0.2
0.4
0.6
0.8
1.0
1.2
27.00 28.00 29.00 30.00 31.00 32.00 33.00 34.00
Wood Duck Usage
Winter Temperature (􀀁􀄩)
R² : 0.029
0.0
0.2
0.4
0.6
0.8
1.0
1.2
47.00 47.50 48.00 48.50 49.00 49.50 50.00 50.50
Wood Duck Usage
Spring Temperature (􀀁􀄩)
R² : 0.021
0.0
0.2
0.4
0.6
0.8
1.0
1.2
37 38 39 40 41 42 43
Wood Duck Usage
6-Month Temperature (􀀁􀄩)
R² : 0.069**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Wood Duck Usage
Hooded Merganser Usage
R² : 0.061**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Wood Duck Usage
Mammal Usage
R² : 0.105**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Wood Duck Usage
Other Bird Usage
R² : 0.015
0.0
0.2
0.4
0.6
0.8
1.0
1.2
175 195 215 235 255 275
Wood Duck Usage
6-Month Precipitation (in)
Figure 5. Correlations between Wood Duck nest box usage with weather, environmental, and competition variables.
R2 values with one (*) indicate significant, Distance to Coast, while values with two (**) show high significance
such as, Mammal, Wood Duck, Other Bird Usage.
12
have a negative relationship (Figure 6). With an increase in competition for the nest boxes there
will be a decrease in Hooded Merganser usage. With an increase in winter precipitation, the nest
box usage of Hooded Mergansers will also decrease (Figure 6). The results from this model
produced the best fit equation where Hooded Merganser usage (h) can be predicted by Wood
Duck usage (w), mammal usage (m), other birds’ usage (b), and winter precipitation (p).
Equation 2. h= -(0.232) w + -(0.323) m + -(0.283) b + -(0.005) p + -0.201
Figure 6. Correlations between Hooded Merganser nest box usage with weather, environmental, and competition
variables. R2 values with one (*) indicate significant, Winter Precipitation, while values with two (**) show high
significance such as, Mammal, Wood Duck, Other Bird Usage.
R² : 0.124
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40 50 60
Hooded Merganser Usage
Distance to Coast (mi)
R² : 0.097
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 500 1,000 1,500
Hooded Merganser Usage
Elevation (ft)
R² : 0.004*
0.0
0.2
0.4
0.6
0.8
1.0
1.2
80 90 100 110 120 130 140
Hooded Merganser Usage
Winter Precipitation (in)
R² : 0.106
0.0
0.2
0.4
0.6
0.8
1.0
1.2
27 29 31 33 35
Hooded Merganser Usage
Winter Temperature (􀀁􀄩)
R² : 0.019
0.0
0.2
0.4
0.6
0.8
1.0
1.2
95 105 115 125 135
Hooded Merganser Usage
Spring Precipitation (in)
R² : 0.010
0.0
0.2
0.4
0.6
0.8
1.0
1.2
47 48 49 50 51
Hooded Merganser Usage
Spring Temperature (􀀁􀄩)
R² : 0.001
0.0
0.2
0.4
0.6
0.8
1.0
1.2
175 195 215 235 255 275
Hooded Merganser Usage
6-Month Precipitation (in)
R² : 0.054
0.0
0.2
0.4
0.6
0.8
1.0
1.2
37 38 39 40 41 42 43
Hooded Merganser Usage
6-Month Temperature (􀀁􀄩)
R² : 0.025**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Hooded Merganser Usage
Mammal Usage
R² : 0.017**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Hooded Merganser Usage
Other Bird Usage
R² : 0.068**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Hooded Merganser Usage
Wood Duck Usage
13
Wood Duck and Hooded Merganser usage over time was graphed with each weather
variable. Winter precipitation and Wood Duck usage experienced peaks in the beginning of the
study period followed by a major drop and slightly descending trend with slight variation (Figure
7A). Precipitation experienced another drop during 2012 and Wood Duck usage increased the
following year by 3%. A clear relationship can be seen with total precipitation from both seasons
until 2011 where the association seems to become inverse. In the earlier years, spring
precipitation had a positive relationship with Wood Duck usage but an inverse relationship
developed in later years. Although no correlation coefficients were significant, spring
precipitation was noticeably higher than most .472 (Table 1). As winter temperature increased,
usage would decrease which can be seen in years 2005 to about 2008 (Figure 7B). An inverse
relationship is apparent excluding years 2012 to 2014 (Figure 7F). Variation found in average
spring temperature has no relationship to Wood Duck usage through all years.
14
Hooded Merganser usage experienced major fluctuations throughout the years observed,
with an overall increase by 2016. Spring precipitation (Figure 8C) gradually decrease throughout
the years with fluctuations while usage increased. A clear inverse relationship was noticeable, in
times where usage is high precipitation is low and vise-versa which is supported by a correlation
coefficient of -.486 (Table 1). The average spring temperature and Hooded Merganser usage
slowly increased with minor deviations found in both trends (Figure 8D). Winter precipitation
seemed to have little effect on Hooded Merganser nest box usage after 2010, although in years
prior there appeared to be a positive relationship. Winter temperature varied through the years
but in no relation to Hooded Merganser usage (Figure 8B). Based on the Pearson correlation
coefficient of .576, there were no significant correlations between any of the variables.
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
70
90
110
130
150
170
Wood Duck Usage
Winter Precipitation (in)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
70
90
110
130
150
170
Wood Duck Usage
Spring Precipitation (in)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
44
45
46
47
48
49
50
51
52
53
54
Wood Duck Usage
Spring Temperature (◦F)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
35
36
37
38
39
40
41
42
43
44
45
Wood Duck Usage
6-Month Temperature (◦F)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
100
150
200
250
300
Wood Duck Usage
6-Month Precipitation (in)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
25
27
29
31
33
35
37
Wood Duck Usage
Winter Temperature (◦F)
Figure 7. Weather variables (dashed) and Wood Duck nest box usage (solid) over time; Winter Precipitation (A),
Winter Temperature (B), Spring Precipitation (C), Spring Temperature (D), 6-Month Precipitation (E), 6-
Month Temperature (F). Winter (December, January, February) Spring (March, April, May)
A
DA
F
A
E
A
C
B
A
15
0.00
0.05
0.10
0.15
0.20
0.25
0.30
50
70
90
110
130
150
170
Hooded Merganser Usage
Winter Precipitation (in)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
25
27
29
31
33
35
37
Hooded Merganser Usage
Winter Temperature (◦F)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
30
32
34
36
38
40
42
44
46
Hooded Merganser Usage
6-Month Temperature (◦F)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
50
100
150
200
250
300
Hooded Merganser Usage
6-Month Precipitation (in)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
42
44
46
48
50
52
54
Hooded Merganser Usage
Spring Temperature (◦F)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
50
70
90
110
130
150
170
Hooded Merganser Usage
Spring Precipitation (in)
Figure 8. Weather variables (dashed) and Hooded Merganser nest box usage (solid) over time; Winter Precipitation
(A), Winter Temperature (B), Spring Precipitation (C), Spring Temperature (D), 6-Month Precipitation (E),
6-Month Temperature (F). Winter (December, January, February) Spring (March, April, May)
Table 1. Correlation Coefficients for Weather Variables with Hooded Merganser and Wood Duck Nest Box
Usage
Winter Precip. Winter Temp. Spring Precip. Spring Temp. 6-Month Precip 6-Month Temp.
Wood Duck Usage 0.185 -0.381 0.472 -0.264 0.410 -0.366
Hooded Merganser Usage -0.191 -0.024 -0.486 0.175 0.091 -0.422
A B
A
C DA
E
A
F
A
16
Discussion
Hooded Merganser nest box usage gradually increased through the given years while
Wood Duck usage has slowly decreased. This noticeable trend can be an indicator that there are
factors not being accounted for in current management practices that are impeding Wood Ducks’
ability to nest each year. Nest boxes are erected to target the growth of Wood Duck populations
throughout the state because they are a harvested species (DEEP, 2012). Ecological traps, as
stated by Patten and Kelly (2010), can occur when an animal selects a habitat over other more
suitable areas that reduces its own fitness. Nest boxes raise the attractiveness of a selection cue in
a given habitat, even those with lower quality (Patten and Kelly, 2010). Placement of the nest
box does not affect the quality of the habitat but rather the ability of the birds to remain hidden
from predators and competition. The cue to nest in an available cavity is present, but the visible
box lowers offspring’s chance of survival. Nest boxes clustered in groups over open bodies of
water do not mimic sporadic cavities hidden in dead standing trees and can lead to an increase
incidence of parasites, as well as increased predation. Nest parasitism, or dump nesting, is the
product of more than one female laying eggs in a nest. Often young females will follow
established nesters to active nests, either to lay eggs and claim ownership or to leave. This
behavior increases when the nest locations are exposed and clustered, becoming too easy for
other females to find (Schlaepfer et al. 2002). A typical clutch, which averages 10–12 eggs, may
grow to 30–50 eggs in a single nest (Schlaepfer et al. 2002; Semel et al. 1988). The excess eggs
generally result in the nests being abandoned, incubated improperly, or with crushed eggs. This
phenomenon could also be occurring at sites located in Connecticut, thus contributing to the
decrease in Wood Duck usage allowing more nesting opportunities for Hooded Mergansers.
Connecticut biologist have recorded multiple boxes with nests containing anywhere from 13-25
17
whole eggs along with 1-28 broken eggs in addition, indicating the nest was abandon early in the
season. Without knowing exact location of boxes at each site, it is difficult to conclude whether
dump nesting is responsible for usage fluctuations throughout the years. In order to properly
identify a dump nest, data such as number of eggs present, beginning of incubation, eggs size
and color to identify species needs to be collected throughout the nesting season.
Vegetation height is critical for nesting Wood Ducks and Hooded Mergansers because
they both require adequate cover for protection from predators. When vegetation composition
and structure is altered it can create an ecological trap (Schlaepfer et al. 2002). An open nest box
attracts an individual to a site while the altered structure of vegetation reduces cover and, in turn,
lowers the quality of surrounding habitat (Patten and Kelly, 2010). When trees and grasses are
cut down or fall over, more edges are created with heterogeneous structure. Wind throw is
common throughout the state of Connecticut, usually stemming from hurricanes and strong
winds, it can drastically change the structure of a habitat by knocking down trees and limbs
(McCarthy, n.d.). Waterfowl may choose sites with fallen trees and damaged cover because an
artificial cavity is provided; these individuals can become more prone to predation (Schlaepfer et
al. 2002).
The further away from the coast the box sites were, the lower Wood Duck usage became.
Although there appeared to be a trend for increasing elevation and lower Wood Duck usage,
when tested this relationship was not statistically significant (Figure 5). Wood Duck are known
to have a preference for inland opposed to coastal wetlands (Metzler and Tiner, 1992). If the nest
box sites (Figure 2) are compared to the plant hardiness zones of Connecticut (Figure 3), three
clear observations can be made. There are no nest box sites located along the coast in the
warmest zone ranging from 0 to 5°F, the majority of sites are found spaced out within the zone
18
ranging from 0 to -5°F, and sites in zones -5 to -15°F are clustered or grouped. These trends can
be attributed to the variability in weather as the distance from the coast, with colder minimums
and warmer maximums (Horton et al. 2014). Although found throughout the state, it is highly
possible Wood Ducks have a preference for wetlands found in the -5 to 0 zone due to low
variability in weather fluctuations and availability of inland wetlands. This can be supported by
the negative relationship between Wood Duck usage spring temperature, spring precipitation,
and winter precipitation (Figure 5). When the weather is more variable with colder minimums,
Wood Ducks are found less in northern sites.
Hooded Merganser nest box usage was found to be inversely related to winter
precipitation. Low winter precipitation has been documented to be correlated with higher diving
duck abundance. In Ontario, 23% of the variation in diving duck population size was attributed
to cooler temperatures in April and lower precipitation in February (Mallory et al. 2003).
Although this study compared each month to waterfowl populations, it supports the idea that
lower precipitation in winter months can lead to higher usage that following nesting season. It is
possible that these lower precipitation levels throughout the winter can have an effect on annual
ice conditions across the state. Colder temperatures indicate snowfall would be present (Figure
6). Due to lack of snow, which acts as an insulating layer, ice coverage can persist longer
through the season. Resident birds are less likely to inhabit areas with little to no water access
and will search for another site, allowing migrating individuals to nest when they arrive (Mallory
et al. 2003). As discussed in the previous paragraph and shown on the USDA plant hardiness
zone map, weather variability increases as distance from the coast increases. Hooded Mergansers
had a positive relationship with both distance to coast and elevation (Figure 6), showing a
preference for inland weather fluctuations. This also can be supported by the negative
19
relationship with winter temperature and Hooded Merganser usage, the lower the temperatures
the higher the usage (Figure 6). Though not found to be significant in the least squares regression
analysis, winter and spring temperatures exhibited opposite trends in relation to Hooded
Merganser nest box usage, where lower winter and higher spring temperatures were associated
with higher populations (Figure 6). Since Hooded Mergansers require deep water bodies, having
warmer temperatures in the spring allows for ice to melt giving way to appropriate feeding
grounds while colder winter temperatures keep the ice on water bodies frozen to deter resident
breeding waterfowl from nesting (Mallory et al. 2003). Wood Ducks may not be significantly
affected by winter precipitation and temperature because their breeding season begins later and
warranting that shallow bodies of water have thawed are abundant with resources (Mallory et al.
2003).
Nest box usage for both species decreased when competition from mammals and other
birds were introduced into the model (Figure 5 and 6). Wood Duck nest box usage was highly
negatively correlated with other bird nest box usage; when other species were found using the
box it was rare to find any sign of a Wood Duck (Figure 5). Dump nesting is an example of both
intra- and inter-specific competition commonly observed in cavity-nesting waterfowl. It is
particularly common amongst birds using nest boxes and is generally lethal to the nest
(Heusmann et al. 1980). Interspecific competition seems to be the main form of rivalry in
Connecticut based on the correlations between Wood Duck usage, other bird, and Hooded
Mergansers (Figure 5 and 6). Attaining reproductive success without experiencing the physical
dangers associated with parental care and incubation advantageous to the females laying eggs in
multiple nests (Semel and Sherman, 1986). However, in areas overcome with dump nesting, the
majority of the nests fail (Semel and Sherman, 1986; Amat, 1987). Since it is known mergansers
20
prefer areas close to rivers and streams (Kitchen and Hunt, 1969), competition for nest boxes in
proximity to sites near moving water could be higher. When Hooded Merganser were present
Wood Duck usage showed a very strong negative relationship and a t-ratio of -3.63, indicating
these two species have a strong competition (Figure 5). The line of best fit indicates that Hooded
Mergansers, on the other hand, were less bothered by Wood Ducks nesting in a site (Figure 6). It
is possible late nesting Hooded Mergansers follow Wood Ducks to established nest boxes and
begin to lay their own eggs. The individual might steal an established nest or continue to deposit
eggs in separate nests until it creates its own (Schlaepfer et al. 2002; Heusmann et al. 1980). Nest
box fidelity, or returning to a previous breeding site, has been observed in both male and female
Wood Ducks (Hepp and Kennamer, 1992; Dugger et al. 1999). Given the similarities between
the two species, Hooded Mergansers may also exhibit this behavior and aid in interspecific
competition for nest boxes. Because Hooded Mergansers begin nesting 2–3 weeks prior to Wood
Ducks, an individual may return same site the nest breeding season.
Limitations to study
The results from this study may not fully estimate the strength of the relationships
between waterfowl nest box usage and weather for several possible reasons. First, this can be
attributed to boxes not being checked consistently, resulting in years without data at multiple
sites. Second. by grouping the nest box usages into proportions a large portion of other species
use at each site, specific nest box information, and other biological information was lost along
with significant relationships that may have been overlooked. Third, weather data came from
several weather stations found in various parts of the state of Connecticut. There is an under
representation of weather stations in the coldest zone, possibly skewing the correlations between
usage and weather variables (Figure 2 and 3.
21
Future Studies
There are many opportunities for further research to be conducted in Connecticut based on
the results of this study. To understand the fluctuations in Wood Duck and Hooded Merganser
nest box usage in Connecticut, nest box placement needs to be assessed. I encourage future
researchers to follow the methods presented in Semel and Sherman (1995) or Semel et al. (1988)
to examine influence of box placement on dump nesting. Banding both Hooded Mergansers and
Wood Ducks that enter nest boxes can record dump nest information, site fidelity, and even
habitat quality. Blums et at. (2002) used long-term mark-recapture studies of banded waterfowl
to assess habitat quality through nest fidelity in three duck species. Future studies for biotic
factors also include examining vegetation structure and diversity at each site to identify regional
patterns in nest box usage.
Weather parameters, such as precipitation and temperature, that dependent on season
should further be analyzed in relation to Wood Duck and Hooded Merganser nest box usage.
Incorporating ice-in and ice-out dates for each nesting site can further explore the relationship
between Hooded Mergansers and winter precipitation. Through integrating methods seen in
Mallory et al. (2003), using monthly weather variables (as opposed to seasonal), tests can reveal
what factors play a role in waterfowl nest box usage. By scaling down to site-specific weather
data a more thorough analysis across the state could be conducted as well.
22
Conclusion and Management Implications
Previous studies have showed that abiotic (precipitation, temperature, distance to coast)
and biotic variables (species competition) play a significant role in Wood Duck and Hooded
Merganser nest box usage (Mallory et al. 2002; Heusmann, 1984; Heusmann et al. 1967; Morse
and Wright, 1969). This study has demonstrated a slight influence of weather variables on nest
box usage, but from these results it cannot be concluded that it is a good predictor. It can be
concluded, however, that Wood Ducks and Hooded Mergansers are not highly sensitive to
deviations in weather. The results presented here, in addition to those presented elsewhere (e.g.,
Mallory et al. 2003) suggest that managers should incorporate weather variables when
conducting Wood Duck and Hooded Merganser population assessments. Furthermore, nest box
placement and dump nesting possibly contribute to the strong negative relationship amongst
competitively nesting species. Nest boxes are currently on both land and water. Boxes found on
land are located 30-150 feet from the water with no major obstacles (e.g. roads, fences, etc.).
Nest boxes built over the water are at least four feet above the high-water level to prevent
flooding and facing toward open water. It is common for boxes to be erected close together and
highly visible for ease of monitoring (NRCS, n.d.). To combat this, managers need to ensure nest
boxes are properly hidden along water bodies with sufficient cover, are at least 600 feet apart,
and are not visible to one another to reduce parasitic nesting (Semel and Sherman, 1995; Semel
et al. 1988; Semel and Sherman, 1986; NRCS, n.d.).
23
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Click tabs to swap between content that is broken into logical sections.

Abiotic and Biotic Correlates of Hooded Merganser and Wood Duck Nest Box Usage
by:
Megan Carroll
A senior thesis submitted in partial fulfillment of the requirements for the degree of
Bachelor of Science
Wildlife and Fisheries Management
At
Unity College
Fall, 2017
i
Abiotic and Biotic Correlates of Hooded Merganser and Wood Duck Nest Box Usage
by:
Megan Carroll
A senior thesis submitted in partial fulfillment of the requirements for the degree of
Bachelor of Science
Wildlife and Fisheries Management
At
Unity College
Fall, 2017
ii
Abstract
Wildlife managers use a variety of management practices to properly sustain harvested
wildlife species in the face of a constantly changing environment. Wood Duck and Hooded
Merganser nest box usage in Connecticut has varied throughout the years 2005–2016. The
overall objectives of this study were to examine potential relationships between weather
variables and species nest box usage in Connecticut and to determine if environmental factors
could predict species usage in the future. Data supplied by the Connecticut Department of
Environmental and Energy Protection and collected from Weather Underground (2017) and
Google Earth Pro (2017) were analyzed using least squares regression and correlation models.
Weather information (winter, spring, 6-month precipitation and temperature), elevation, distance
to coast, and competition usage were compared. Hooded Merganser nest box usage gradually
increased while Wood Duck usage showed a slight decrease. Distance from the coast was
significant for Wood Duck usage. Hooded Merganser nest box usage was found to be inversely
related to winter precipitation. Nest box usage for both species decreased when competition from
mammals and other birds was added. A slight influence of weather variables on nest box usage
was noted, but it cannot be concluded that weather is a good predictor. Nest box placement and
dump nesting possibly contribute to the strong negative relationship amongst competitively
nesting species. To combat this, managers need to ensure nest boxes are properly hidden along
water bodies with sufficient cover to reduce parasitic nesting.
iii
Acknowledgements
I want to thank my advisors, Kevin Spigel and Matthew Chatfield, for taking time out
their schedules to meet weekly and work through every problem I encountered from the
beginning. Their encouragement, humor, understanding, and knowledge helped me through this
past year develop a working thesis. Second, Aimee Phillippi for reviewing every single one of
my drafts and being flexible throughout the process as my professor as well. Third, Brent Bibles
for constant encouragement as well as answering every question, even though it was not
required. Fourth, Connecticut State Biologist Kelly Kubik for originally sparking my interest in
the topic studied, expressing interest, and supplying the waterfowl data. Fifth, my roommates,
Amanda Griswold and Cassidy Marshall for assisting in the early stages of data organization and
GIS assistance. Lastly, Cole Arsenault, Greg LcClair, Marlea Naples, Wesley Franco, and family
for providing moral support through the past year.
iv
Table of Contents
LIST OF TABLES ............................................................................................................................. V
LIST OF FIGURES .......................................................................................................................... VI
INTRODUCTION ............................................................................................................................... 1
METHODS ........................................................................................................................................ 7
DATA COLLECTION ................................................................................................................................... 7
DATA ANALYSIS ......................................................................................................................................... 9
RESULTS ........................................................................................................................................ 10
DISCUSSION ................................................................................................................................... 16
LIMITATIONS TO STUDY ............................................................................................................................ 20
FUTURE STUDIES ................................................................................................................................... 21
CONCLUSION AND MANAGEMENT IMPLICATIONS .............................................................. 22
REFERENCES ................................................................................................................................ 23
v
List of Tables
Table 1. Correlation Coefficients for Weather Variables and Nest Box Usage ………………15
vi
List of Figures
Figure 1. Wood Duck and Hooded Merganser Distribution in North America ……………...….2
Figure 2. ArcGIS Map of Sites and Weather Stations …………………………..……………….3
Figure 3. USDA Connecticut Plant Hardiness Zones …………………………………………....4
Figure 4. Wood Duck and Hooded Merganser Usage Over Time ……………………………...10
Figure 5. Wood Duck Correlation Graphs ………………………………………….…………..11
Figure 6. Hooded Merganser Correlation Graphs ………………………………………………12
Figure 7. Wood Duck Line Graphs ……………………………………………………………..14
Figure 8. Hooded Merganser Line Graphs ……………………………………………………...1
1
Introduction
Wildlife managers rely on a variety of management practices in order to properly sustain
harvested wildlife species in the face of a constantly changing environment. Hunting is a
widespread management tactic utilized to maintain a healthy population because it is cheap,
effective, and involves the general public. It is crucial for wildlife biologists to avoid high
harvest quotas that could result in additive mortality since an overharvested population will not
be able to sustain itself over time (Sandercock et al. 2011). Large population sizes and numerous
stakeholders in North America result in waterfowl being extensively studied (Batt et al. 1992).
Lengthy regulatory processes require data collection on population sizes, harvest levels,
production, and migration in order to pass new regulations (Johnson and Williams, 1995).
Despite the large investment in studying these biotic factors influencing population sizes, abiotic
factors, such as weather, historically have been overlooked in population assessment practices
(Heusamnn, 1984). More recently, adaptive waterfowl harvest management techniques have
been introduced which are based on well-defined objectives that account for uncertainty like
uncontrolled environmental factors, such as storms or other weather events (Johnson and
Williams, 1995).
Waterfowl are organized into two functional groups. Dabbling ducks, like Wood Ducks
(Aix sponsa), Blue-Winged Teal (Anas discors) and Mallards (Anas platryhynchos), feed off the
water’s surface. Diving ducks, like Hooded Mergansers (Lophodytes cucullatus), Buffleheads
(Bucephala albeola), and Ring-Necked Ducks (Aythya collaris), swim underwater to find food.
Wood Duck populations are found in eastern and western ranges, divided by the Great Plains and
multiple deserts (Fielder, 2000). Their breeding ranges are found in more northern areas, some of
which overlap with their year-round habitat, but can also be found breeding in southern regions
2
(Figure 1). Naturally occurring breeding habitat is found throughout southern parts of Canada
and extends south to Florida on the east coast, and along the shoreline of California on the west
coast. Although arrival times may vary between states, Wood Ducks are present in Connecticut
from March to November. The breeding season can begin in early March, but generally will not
start until April (Fielder, 2000; DEEP, 2012). Wood Ducks are well distributed throughout North
America while Hooded Mergansers are less commonly found (Heusmann et al. 2000). With
breeding and wintering distributions similar to those of Wood Ducks, Hooded Mergansers are
found in the same habitats, but generally in lower densities (Morse et al. 1969; Heusmann et al.
2000). Hooded Merganser breeding ranges extend throughout the east and the Pacific Northwest
but can be found regularly in the Great Lakes region (Figure 1). In Connecticut, Hooded
Mergansers begin nesting in late February to April (Morse et al. 1969).
Figure 1. Wood Duck and Hooded Merganser distribution and migratory patterns throughout North America.
Noting the similar coverage year-round (purple) along the East Coast. Maps modified from Cornell Lab of
Ornithology; data courtesy of NatureServe.
3
Wood Ducks and Hooded Mergansers are both cavity nesting species and require wooded
nesting sites close to water, with trees .3048-.6096 meters in diameter with pre-formed cavities
(Cornell University, 2015). Appropriate breeding sites consist of forested wetlands with trees
that provide cavities necessary for nesting and offer the birds with adequate cover (e.g., fallen
trees, shrubs, herbaceous plants). Areas with 50-75% cover are preferred to allow adequate
forage but also avoidance from predation (Cornell University, 2015). Both species nest near
bodies of water due to diets compromised heavily on aquatic plants and invertebrates (Fielder,
2000; Heusmann et al. 2000). Wood Duck diet varies seasonally, but includes acorns, panic grass
(Panisum), pondweed (Potamogeton), duckweed (Lemnoideae), and white waterlily (Nymphaea
alba) year-round (Drobney, 1980). Before egg-laying, females feed on invertebrates in major
taxonomic groups, such as Odonata, Diptera, Lepidoptera, Hemiptera, and Isopoda because they
are rich in calcium and protein (Drobney, 1980). Because of their feeding behavior, the Hooded
Merganser’s diet primarily consists of fish, crayfish, aquatic insects, amphibians, and some
vegetation (Dugger et al. 1994).
Both species pair with their mates before reaching the desired nesting site. Females make
the final nest selection primarily based on proximity to water (Morse et al. 1969). Male Wood
Ducks accompany their mates when searching for a cavity, but wait nearby while females
investigate each hole (Manlove and Hepp, 2000; Fielder, 2000); male Hooded Mergansers are
not known to play a role in nest selection (Dugger et al. 1994).
Due to extended hunting seasons, market shooting, and habitat loss in the early 1900s,
Wood Ducks were close to extinction in North America (DEEP, 2012). Hooded Mergansers also
suffered a decrease in population size around the same time as a result of logging, which reduces
nesting cavities (Dugger et al. 1994). With the aid of the Migratory Bird Treaty Act in 1918,
4
commercial hunting was banned, hunting seasons were not to exceed 3.5 months, and bag limits
were adjusted (Johnson and Williams, 1999). Management efforts, including the installation of
nest boxes and restoration of habitat, have boosted both species’ populations (DEEP, 2012) and
allowed for expansion throughout their historic ranges (Dugger et al. 1994).
Natural cavities are formed by woodpeckers and natural decay in large deciduous trees
found in old growth woodlots (Fielder, 2000). In most cases, these cavities are short-lived
because host trees are often blown down by strong winds or are taken by other species, leaving
cavity-nesting ducks with minimal nesting sites. To combat this issue, nest boxes are used as an
inexpensive substitution to support waterfowl populations such as Hooded Mergansers, common
mergansers, Wood Ducks, common golden eyes, barrow’s golden eyes, and buffleheads (Porter
et al. 2008). Nest boxes substitute for natural cavities and expand breeding sites, resulting in
increased Wood Duck and Hooded Merganser populations (Bellrose et al. 1964; DEEP, 2012).
Nest box installation is not limited to state agencies and biologists; many private property
owners, the majority of stakeholders, have participated in the conservation practice. The extra
nesting sites have created natural competition by other cavity nesting species posing an issue for
target species management. For example, in Arrowwood National Wildlife Refuge in North
Dakota, nest boxes were erected in 1968 to support a newly added population of hand-reared
Wood Ducks into the area (Doty et al. 1984). The birds became an established breeding
population and prominent on the refuge by 1969. The Wood Duck population continued to rise
until 1975 when it began to decline. Hooded Mergansers were first recorded using the nest boxes
in 1973 and by 1982 their nesting attempts surpassed the Wood Duck. Dual nesting, separate
individuals laying eggs in the same nest, began in 1977 and rapidly increased. Hooded
Mergansers are known to lay eggs in nests that belong to both other mergansers and Wood
5
Ducks. Data suggest mergansers became the dominant species in the refuge following the
addition of next boxes (Doty et al. 1984).
Nest boxes are only one habitat related factor that can impact waterfowl population
numbers. For example, the Massachusetts Division for Fisheries and Wildlife analyzed data
covering years 1979 to 1998 and found a 289% increase in hatching success and a 225% increase
in population size. The agency attributed this growth to changes in hunting regulations, improved
habitat, and a rise in beaver populations which resulted in more, small wooded ponds that extend
ideal foraging habitat (Heusmann et al. 2000). Biotic factors such as these are commonly a part
of by management practices in order to alter a targeted species population. In some cases,
controlling biotic factors may have no overall effect.
Unusual weather conditions may also impact duck populations and, as a result, influence
management plans. For example, the effects of abnormal weather on Wood Duck production
during 1982 in Massachusetts led to a decline in reproductive success. Abnormal weather events
in this study were defined as late snowstorms, heavy rainfall, and prevailing cold temperatures.
The decline in reproductive success was evident through smaller broods, which were caused by
reduced nest success and fewer eggs hatching in successful nests (Heusmann, 1984).
While several small storms can have a negative impact on the nest success of local
waterfowl, weather events covering a larger area will impact multiple waterfowl species’
breeding populations. For example, Mallory et al. (2003) evaluated trends in population size and
reproductive success of waterfowl species in northwest Ontario, Canada. The team used existing
waterfowl and weather data to determine if annual or regional weather conditions can cause
variation in annual estimates of waterfowl breeding populations. Weather variables explained 9–
17% of variation in abundance of dabbling ducks with higher duck abundance in years with
6
cooler February and April temperatures and higher April precipitation. For diving ducks, weather
variables explained 12–36% of variation in abundance with higher populations in years when
April was cool and February was relatively dry. Overall, weather conditions in the winter and
early spring explain some variation in annual estimates of breeding waterfowl. This study shows
that the incorporation of regional weather data into population models may provide correction
factors for waterfowl estimates and, in turn, allow managers to have a better understanding of
population trends.
Wood Duck and Hooded Merganser nest box usage in Connecticut varied throughout the
years 2005–2016, specifically with an observed increase in the Hooded Merganser population.
This increase can also be observed in Maine, New York, New Hampshire, and Vermont
(Heusmann et al. 2000). There has been no recent research suggesting why this fluctuation has
occurred or what could be the driving factors. Variation in temperature and precipitation in
months preceding nesting season has negatively influenced the abundance of waterfowl as seen
in multiple studies causing these variables to be a concern for future management purposes
(Mallory et al. 2003; Heusmann, 1984; Schummer et al. 2010). The overall objectives of this
study were to examine potential relationships between weather variables and species nest box
usage in Connecticut and to determine if environmental factors could predict species usage in the
future.
7
Methods
Data collection
The nest box data used for this study were collected by biologists and volunteers from
2005–2016 during winter months and provided by the Connecticut Department of Environmental
and Energy Protection (DEEP). Monthly temperature averages and monthly sum of precipitation
for the years 2005–2016 were collected from Weather Underground (2017) from 14 weather
stations in Connecticut, Rhode Island, Massachusetts, and New York (Figure 2). Precipitation
data were recorded from rainfall and rainfall equivalent in snow since there was no specified
form listed. Distance to the coast and elevation data were recorded for each site using Google
Earth Pro (2017).
Data consisted of the following information for each nest box: town, site, district, box
number, years checked, and years used. There were 163 sites located throughout the state of
Connecticut that were analyzed. Boxes were considered used if any sign of life was noted
Figure 2. ArcGIS map of FAA weather stations (X) and nest box sites (dots) located across the state
of Connecticut.
Atlantic Ocean
NY
MA
RI
8
including broken or whole eggs, down, membranes, and/or dead chicks. Due to inconsistent data
collection records, data were standardized by combining all nest boxes within a site. To maintain
the integrity of the original data set, majority use of a given species (51%) was used as an
organization technique. By condensing the boxes at each site and classifying each year by a
given species use, a more complete record was developed. Weather data were condensed into
two seasons: winter (December, January, February) and spring (March, April, May).
Temperatures were averaged within each season and the sum of precipitation was found.
Coordinates for each site and weather station were entered into ArcGIS and analyzed. Using
Thiessen polygons were created to assign each site to the closest weather station. A map created
by the United States Department of Agriculture (USDA) indicating plant hardiness zones in
Connecticut naturally divides the state by average annual extreme minimum temperatures
(Figure 3). These zones allowed the comparison of trends in the data to weather patterns.
Figure 3. Plant hardiness zones of Connecticut and Rhode Island as described by the average annual extreme
minimum temperatures between years 1976 to 2005 (USDA, 2012).
9
Data analysis
Least squares regression was used to calculate possible climate predictors for Wood
Ducks and Hooded Mergansers. This test was chosen to help determine changes in nest box use
by the remaining abiotic and biotic variables because of its ability to predict future values for one
variable when another’s value is unknown. By condensing the use (Wood Duck, Hooded
Merganser, other bird, mammal, no use) for each site into a proportion, years where data was not
collected were removed. Weather information (winter, spring, 6-month precipitation and
temperature) were treated as independent variables along with elevation, distance to coast, and
competition usage. The resulting p-values from this test were assessed at an alpha-level of .05.
Seasonal weather variables and waterfowl nest box usage were compared to evaluate any
possible correlations over time. Although a small dataset of only twelve records was used, the
resulting graphs gave a visual of any trend through the years. First Hooded Merganser and Wood
Duck usage were compared to understand how the two species have interacted throughout the
years. Next, graphs were created for both to show individual relationships between usage and
each weather variable. A correlation analysis verified any possible relationship. The data was
graphed and analyzed on excel, using the function “correl” to determine the correlation
coefficients. Each correlation coefficient was compared to the Pearson correlation coefficient of
.576 found based on 12 ordered pairs.
10
Results
Hooded Merganser and Wood Duck nest box usage did not show a significant correlation
between 2005–2016 (Figure 4). Wood Duck usage was consistently higher than Hooded
Merganser, but Hooded Merganser usage seemed to be increasing. Wood Duck usage remains
stable after 2008 while Hooded Merganser usage experiences more variability. The two greatest
annual increases in usage by mergansers are accompanied by large decreases in Wood Duck
usage as seen in years 2008 and 2014.
The results from the least squares regression model from Wood Duck nest usage with
weather, environmental, and competition factors, showed Hooded Merganser (t = -3.63; p =
0.0004), mammal (t = -5.68; p = <0.0001), other bird (t = -5.43; p = <0.0001), and distance to
coast (t = -2.52; p = 0.0128) were significant. Spring precipitation was not considered significant
with a p-value of 0.1889 but exhibited a weak negative trend (Figure 5). All significant variables
found in this test have a strong inverse relationship with Wood Duck nest box usage. As
competition usage and miles from coast increase, Wood Duck usage decreases (Figure 5). This
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Nest Box Usage
Figure 4. Wood Duck (dashed) and Hooded Merganser (solid) usage over
11
model resulted in a final equation where Wood Duck usage (w) can be predicted by Hooded
Merganser usage (h), mammal usage (m), other birds’ usage (b), and distance to coast (d).
Equation 1. w= -(0.347) h + -(0.798) m + -(0.556) b + -(.008) d + 1.894
The report for Hooded Merganser usage consisting of weather, environmental, and
competition factors resulted with Wood Duck (t = -3.63; p = 0.0004), mammal (t = -2.61; p =
0.0100), other bird (t = -3.19; p = 0.0017), and winter precipitation (t = -2.50; p = 0.0136) as
significant at the alpha-level of 0.05. All variables associated with Hooded Merganser usage
R² : 0.139*
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 20 40 60 80
Wood Duck Usage
Distance to Coast (mi)
R² : 0.007
0.0
0.2
0.4
0.6
0.8
1.0
1.2
75 95 115 135 155
Wood Duck Usage
Winter Precipitation (in)
R² : 0.099
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 500 1000 1500 2000
Wood Duck Usage
Elevation (ft)
R² : 0.022
0.0
0.2
0.4
0.6
0.8
1.0
1.2
95 105 115 125 135 145
Wood Duck Usage
Spring Precipitation (in)
R² : 0.072
0.0
0.2
0.4
0.6
0.8
1.0
1.2
27.00 28.00 29.00 30.00 31.00 32.00 33.00 34.00
Wood Duck Usage
Winter Temperature (􀀁􀄩)
R² : 0.029
0.0
0.2
0.4
0.6
0.8
1.0
1.2
47.00 47.50 48.00 48.50 49.00 49.50 50.00 50.50
Wood Duck Usage
Spring Temperature (􀀁􀄩)
R² : 0.021
0.0
0.2
0.4
0.6
0.8
1.0
1.2
37 38 39 40 41 42 43
Wood Duck Usage
6-Month Temperature (􀀁􀄩)
R² : 0.069**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Wood Duck Usage
Hooded Merganser Usage
R² : 0.061**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Wood Duck Usage
Mammal Usage
R² : 0.105**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Wood Duck Usage
Other Bird Usage
R² : 0.015
0.0
0.2
0.4
0.6
0.8
1.0
1.2
175 195 215 235 255 275
Wood Duck Usage
6-Month Precipitation (in)
Figure 5. Correlations between Wood Duck nest box usage with weather, environmental, and competition variables.
R2 values with one (*) indicate significant, Distance to Coast, while values with two (**) show high significance
such as, Mammal, Wood Duck, Other Bird Usage.
12
have a negative relationship (Figure 6). With an increase in competition for the nest boxes there
will be a decrease in Hooded Merganser usage. With an increase in winter precipitation, the nest
box usage of Hooded Mergansers will also decrease (Figure 6). The results from this model
produced the best fit equation where Hooded Merganser usage (h) can be predicted by Wood
Duck usage (w), mammal usage (m), other birds’ usage (b), and winter precipitation (p).
Equation 2. h= -(0.232) w + -(0.323) m + -(0.283) b + -(0.005) p + -0.201
Figure 6. Correlations between Hooded Merganser nest box usage with weather, environmental, and competition
variables. R2 values with one (*) indicate significant, Winter Precipitation, while values with two (**) show high
significance such as, Mammal, Wood Duck, Other Bird Usage.
R² : 0.124
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40 50 60
Hooded Merganser Usage
Distance to Coast (mi)
R² : 0.097
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 500 1,000 1,500
Hooded Merganser Usage
Elevation (ft)
R² : 0.004*
0.0
0.2
0.4
0.6
0.8
1.0
1.2
80 90 100 110 120 130 140
Hooded Merganser Usage
Winter Precipitation (in)
R² : 0.106
0.0
0.2
0.4
0.6
0.8
1.0
1.2
27 29 31 33 35
Hooded Merganser Usage
Winter Temperature (􀀁􀄩)
R² : 0.019
0.0
0.2
0.4
0.6
0.8
1.0
1.2
95 105 115 125 135
Hooded Merganser Usage
Spring Precipitation (in)
R² : 0.010
0.0
0.2
0.4
0.6
0.8
1.0
1.2
47 48 49 50 51
Hooded Merganser Usage
Spring Temperature (􀀁􀄩)
R² : 0.001
0.0
0.2
0.4
0.6
0.8
1.0
1.2
175 195 215 235 255 275
Hooded Merganser Usage
6-Month Precipitation (in)
R² : 0.054
0.0
0.2
0.4
0.6
0.8
1.0
1.2
37 38 39 40 41 42 43
Hooded Merganser Usage
6-Month Temperature (􀀁􀄩)
R² : 0.025**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Hooded Merganser Usage
Mammal Usage
R² : 0.017**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Hooded Merganser Usage
Other Bird Usage
R² : 0.068**
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Hooded Merganser Usage
Wood Duck Usage
13
Wood Duck and Hooded Merganser usage over time was graphed with each weather
variable. Winter precipitation and Wood Duck usage experienced peaks in the beginning of the
study period followed by a major drop and slightly descending trend with slight variation (Figure
7A). Precipitation experienced another drop during 2012 and Wood Duck usage increased the
following year by 3%. A clear relationship can be seen with total precipitation from both seasons
until 2011 where the association seems to become inverse. In the earlier years, spring
precipitation had a positive relationship with Wood Duck usage but an inverse relationship
developed in later years. Although no correlation coefficients were significant, spring
precipitation was noticeably higher than most .472 (Table 1). As winter temperature increased,
usage would decrease which can be seen in years 2005 to about 2008 (Figure 7B). An inverse
relationship is apparent excluding years 2012 to 2014 (Figure 7F). Variation found in average
spring temperature has no relationship to Wood Duck usage through all years.
14
Hooded Merganser usage experienced major fluctuations throughout the years observed,
with an overall increase by 2016. Spring precipitation (Figure 8C) gradually decrease throughout
the years with fluctuations while usage increased. A clear inverse relationship was noticeable, in
times where usage is high precipitation is low and vise-versa which is supported by a correlation
coefficient of -.486 (Table 1). The average spring temperature and Hooded Merganser usage
slowly increased with minor deviations found in both trends (Figure 8D). Winter precipitation
seemed to have little effect on Hooded Merganser nest box usage after 2010, although in years
prior there appeared to be a positive relationship. Winter temperature varied through the years
but in no relation to Hooded Merganser usage (Figure 8B). Based on the Pearson correlation
coefficient of .576, there were no significant correlations between any of the variables.
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
70
90
110
130
150
170
Wood Duck Usage
Winter Precipitation (in)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
70
90
110
130
150
170
Wood Duck Usage
Spring Precipitation (in)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
44
45
46
47
48
49
50
51
52
53
54
Wood Duck Usage
Spring Temperature (◦F)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
35
36
37
38
39
40
41
42
43
44
45
Wood Duck Usage
6-Month Temperature (◦F)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
100
150
200
250
300
Wood Duck Usage
6-Month Precipitation (in)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
25
27
29
31
33
35
37
Wood Duck Usage
Winter Temperature (◦F)
Figure 7. Weather variables (dashed) and Wood Duck nest box usage (solid) over time; Winter Precipitation (A),
Winter Temperature (B), Spring Precipitation (C), Spring Temperature (D), 6-Month Precipitation (E), 6-
Month Temperature (F). Winter (December, January, February) Spring (March, April, May)
A
DA
F
A
E
A
C
B
A
15
0.00
0.05
0.10
0.15
0.20
0.25
0.30
50
70
90
110
130
150
170
Hooded Merganser Usage
Winter Precipitation (in)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
25
27
29
31
33
35
37
Hooded Merganser Usage
Winter Temperature (◦F)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
30
32
34
36
38
40
42
44
46
Hooded Merganser Usage
6-Month Temperature (◦F)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
50
100
150
200
250
300
Hooded Merganser Usage
6-Month Precipitation (in)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
42
44
46
48
50
52
54
Hooded Merganser Usage
Spring Temperature (◦F)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
50
70
90
110
130
150
170
Hooded Merganser Usage
Spring Precipitation (in)
Figure 8. Weather variables (dashed) and Hooded Merganser nest box usage (solid) over time; Winter Precipitation
(A), Winter Temperature (B), Spring Precipitation (C), Spring Temperature (D), 6-Month Precipitation (E),
6-Month Temperature (F). Winter (December, January, February) Spring (March, April, May)
Table 1. Correlation Coefficients for Weather Variables with Hooded Merganser and Wood Duck Nest Box
Usage
Winter Precip. Winter Temp. Spring Precip. Spring Temp. 6-Month Precip 6-Month Temp.
Wood Duck Usage 0.185 -0.381 0.472 -0.264 0.410 -0.366
Hooded Merganser Usage -0.191 -0.024 -0.486 0.175 0.091 -0.422
A B
A
C DA
E
A
F
A
16
Discussion
Hooded Merganser nest box usage gradually increased through the given years while
Wood Duck usage has slowly decreased. This noticeable trend can be an indicator that there are
factors not being accounted for in current management practices that are impeding Wood Ducks’
ability to nest each year. Nest boxes are erected to target the growth of Wood Duck populations
throughout the state because they are a harvested species (DEEP, 2012). Ecological traps, as
stated by Patten and Kelly (2010), can occur when an animal selects a habitat over other more
suitable areas that reduces its own fitness. Nest boxes raise the attractiveness of a selection cue in
a given habitat, even those with lower quality (Patten and Kelly, 2010). Placement of the nest
box does not affect the quality of the habitat but rather the ability of the birds to remain hidden
from predators and competition. The cue to nest in an available cavity is present, but the visible
box lowers offspring’s chance of survival. Nest boxes clustered in groups over open bodies of
water do not mimic sporadic cavities hidden in dead standing trees and can lead to an increase
incidence of parasites, as well as increased predation. Nest parasitism, or dump nesting, is the
product of more than one female laying eggs in a nest. Often young females will follow
established nesters to active nests, either to lay eggs and claim ownership or to leave. This
behavior increases when the nest locations are exposed and clustered, becoming too easy for
other females to find (Schlaepfer et al. 2002). A typical clutch, which averages 10–12 eggs, may
grow to 30–50 eggs in a single nest (Schlaepfer et al. 2002; Semel et al. 1988). The excess eggs
generally result in the nests being abandoned, incubated improperly, or with crushed eggs. This
phenomenon could also be occurring at sites located in Connecticut, thus contributing to the
decrease in Wood Duck usage allowing more nesting opportunities for Hooded Mergansers.
Connecticut biologist have recorded multiple boxes with nests containing anywhere from 13-25
17
whole eggs along with 1-28 broken eggs in addition, indicating the nest was abandon early in the
season. Without knowing exact location of boxes at each site, it is difficult to conclude whether
dump nesting is responsible for usage fluctuations throughout the years. In order to properly
identify a dump nest, data such as number of eggs present, beginning of incubation, eggs size
and color to identify species needs to be collected throughout the nesting season.
Vegetation height is critical for nesting Wood Ducks and Hooded Mergansers because
they both require adequate cover for protection from predators. When vegetation composition
and structure is altered it can create an ecological trap (Schlaepfer et al. 2002). An open nest box
attracts an individual to a site while the altered structure of vegetation reduces cover and, in turn,
lowers the quality of surrounding habitat (Patten and Kelly, 2010). When trees and grasses are
cut down or fall over, more edges are created with heterogeneous structure. Wind throw is
common throughout the state of Connecticut, usually stemming from hurricanes and strong
winds, it can drastically change the structure of a habitat by knocking down trees and limbs
(McCarthy, n.d.). Waterfowl may choose sites with fallen trees and damaged cover because an
artificial cavity is provided; these individuals can become more prone to predation (Schlaepfer et
al. 2002).
The further away from the coast the box sites were, the lower Wood Duck usage became.
Although there appeared to be a trend for increasing elevation and lower Wood Duck usage,
when tested this relationship was not statistically significant (Figure 5). Wood Duck are known
to have a preference for inland opposed to coastal wetlands (Metzler and Tiner, 1992). If the nest
box sites (Figure 2) are compared to the plant hardiness zones of Connecticut (Figure 3), three
clear observations can be made. There are no nest box sites located along the coast in the
warmest zone ranging from 0 to 5°F, the majority of sites are found spaced out within the zone
18
ranging from 0 to -5°F, and sites in zones -5 to -15°F are clustered or grouped. These trends can
be attributed to the variability in weather as the distance from the coast, with colder minimums
and warmer maximums (Horton et al. 2014). Although found throughout the state, it is highly
possible Wood Ducks have a preference for wetlands found in the -5 to 0 zone due to low
variability in weather fluctuations and availability of inland wetlands. This can be supported by
the negative relationship between Wood Duck usage spring temperature, spring precipitation,
and winter precipitation (Figure 5). When the weather is more variable with colder minimums,
Wood Ducks are found less in northern sites.
Hooded Merganser nest box usage was found to be inversely related to winter
precipitation. Low winter precipitation has been documented to be correlated with higher diving
duck abundance. In Ontario, 23% of the variation in diving duck population size was attributed
to cooler temperatures in April and lower precipitation in February (Mallory et al. 2003).
Although this study compared each month to waterfowl populations, it supports the idea that
lower precipitation in winter months can lead to higher usage that following nesting season. It is
possible that these lower precipitation levels throughout the winter can have an effect on annual
ice conditions across the state. Colder temperatures indicate snowfall would be present (Figure
6). Due to lack of snow, which acts as an insulating layer, ice coverage can persist longer
through the season. Resident birds are less likely to inhabit areas with little to no water access
and will search for another site, allowing migrating individuals to nest when they arrive (Mallory
et al. 2003). As discussed in the previous paragraph and shown on the USDA plant hardiness
zone map, weather variability increases as distance from the coast increases. Hooded Mergansers
had a positive relationship with both distance to coast and elevation (Figure 6), showing a
preference for inland weather fluctuations. This also can be supported by the negative
19
relationship with winter temperature and Hooded Merganser usage, the lower the temperatures
the higher the usage (Figure 6). Though not found to be significant in the least squares regression
analysis, winter and spring temperatures exhibited opposite trends in relation to Hooded
Merganser nest box usage, where lower winter and higher spring temperatures were associated
with higher populations (Figure 6). Since Hooded Mergansers require deep water bodies, having
warmer temperatures in the spring allows for ice to melt giving way to appropriate feeding
grounds while colder winter temperatures keep the ice on water bodies frozen to deter resident
breeding waterfowl from nesting (Mallory et al. 2003). Wood Ducks may not be significantly
affected by winter precipitation and temperature because their breeding season begins later and
warranting that shallow bodies of water have thawed are abundant with resources (Mallory et al.
2003).
Nest box usage for both species decreased when competition from mammals and other
birds were introduced into the model (Figure 5 and 6). Wood Duck nest box usage was highly
negatively correlated with other bird nest box usage; when other species were found using the
box it was rare to find any sign of a Wood Duck (Figure 5). Dump nesting is an example of both
intra- and inter-specific competition commonly observed in cavity-nesting waterfowl. It is
particularly common amongst birds using nest boxes and is generally lethal to the nest
(Heusmann et al. 1980). Interspecific competition seems to be the main form of rivalry in
Connecticut based on the correlations between Wood Duck usage, other bird, and Hooded
Mergansers (Figure 5 and 6). Attaining reproductive success without experiencing the physical
dangers associated with parental care and incubation advantageous to the females laying eggs in
multiple nests (Semel and Sherman, 1986). However, in areas overcome with dump nesting, the
majority of the nests fail (Semel and Sherman, 1986; Amat, 1987). Since it is known mergansers
20
prefer areas close to rivers and streams (Kitchen and Hunt, 1969), competition for nest boxes in
proximity to sites near moving water could be higher. When Hooded Merganser were present
Wood Duck usage showed a very strong negative relationship and a t-ratio of -3.63, indicating
these two species have a strong competition (Figure 5). The line of best fit indicates that Hooded
Mergansers, on the other hand, were less bothered by Wood Ducks nesting in a site (Figure 6). It
is possible late nesting Hooded Mergansers follow Wood Ducks to established nest boxes and
begin to lay their own eggs. The individual might steal an established nest or continue to deposit
eggs in separate nests until it creates its own (Schlaepfer et al. 2002; Heusmann et al. 1980). Nest
box fidelity, or returning to a previous breeding site, has been observed in both male and female
Wood Ducks (Hepp and Kennamer, 1992; Dugger et al. 1999). Given the similarities between
the two species, Hooded Mergansers may also exhibit this behavior and aid in interspecific
competition for nest boxes. Because Hooded Mergansers begin nesting 2–3 weeks prior to Wood
Ducks, an individual may return same site the nest breeding season.
Limitations to study
The results from this study may not fully estimate the strength of the relationships
between waterfowl nest box usage and weather for several possible reasons. First, this can be
attributed to boxes not being checked consistently, resulting in years without data at multiple
sites. Second. by grouping the nest box usages into proportions a large portion of other species
use at each site, specific nest box information, and other biological information was lost along
with significant relationships that may have been overlooked. Third, weather data came from
several weather stations found in various parts of the state of Connecticut. There is an under
representation of weather stations in the coldest zone, possibly skewing the correlations between
usage and weather variables (Figure 2 and 3.
21
Future Studies
There are many opportunities for further research to be conducted in Connecticut based on
the results of this study. To understand the fluctuations in Wood Duck and Hooded Merganser
nest box usage in Connecticut, nest box placement needs to be assessed. I encourage future
researchers to follow the methods presented in Semel and Sherman (1995) or Semel et al. (1988)
to examine influence of box placement on dump nesting. Banding both Hooded Mergansers and
Wood Ducks that enter nest boxes can record dump nest information, site fidelity, and even
habitat quality. Blums et at. (2002) used long-term mark-recapture studies of banded waterfowl
to assess habitat quality through nest fidelity in three duck species. Future studies for biotic
factors also include examining vegetation structure and diversity at each site to identify regional
patterns in nest box usage.
Weather parameters, such as precipitation and temperature, that dependent on season
should further be analyzed in relation to Wood Duck and Hooded Merganser nest box usage.
Incorporating ice-in and ice-out dates for each nesting site can further explore the relationship
between Hooded Mergansers and winter precipitation. Through integrating methods seen in
Mallory et al. (2003), using monthly weather variables (as opposed to seasonal), tests can reveal
what factors play a role in waterfowl nest box usage. By scaling down to site-specific weather
data a more thorough analysis across the state could be conducted as well.
22
Conclusion and Management Implications
Previous studies have showed that abiotic (precipitation, temperature, distance to coast)
and biotic variables (species competition) play a significant role in Wood Duck and Hooded
Merganser nest box usage (Mallory et al. 2002; Heusmann, 1984; Heusmann et al. 1967; Morse
and Wright, 1969). This study has demonstrated a slight influence of weather variables on nest
box usage, but from these results it cannot be concluded that it is a good predictor. It can be
concluded, however, that Wood Ducks and Hooded Mergansers are not highly sensitive to
deviations in weather. The results presented here, in addition to those presented elsewhere (e.g.,
Mallory et al. 2003) suggest that managers should incorporate weather variables when
conducting Wood Duck and Hooded Merganser population assessments. Furthermore, nest box
placement and dump nesting possibly contribute to the strong negative relationship amongst
competitively nesting species. Nest boxes are currently on both land and water. Boxes found on
land are located 30-150 feet from the water with no major obstacles (e.g. roads, fences, etc.).
Nest boxes built over the water are at least four feet above the high-water level to prevent
flooding and facing toward open water. It is common for boxes to be erected close together and
highly visible for ease of monitoring (NRCS, n.d.). To combat this, managers need to ensure nest
boxes are properly hidden along water bodies with sufficient cover, are at least 600 feet apart,
and are not visible to one another to reduce parasitic nesting (Semel and Sherman, 1995; Semel
et al. 1988; Semel and Sherman, 1986; NRCS, n.d.).
23
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